I think he and his client were hoping for a big pay-day after the contract extension. A few clubs been monitoring him and Arsenal did try and get him for £30-40m after winning the league if I am not mistaken. Backfired a little, but I am quite sure come summer he will be moving on for about £40-50m, the market rate for an attacking midfielder like him. If he recaptures his form during their title run, I think his price tag will soar towards the £70m range.Mahrez' agent will have made very little from him to date, and is quite possibly more upset by the collapse of the deal than Mahrez himself.
Does make you wonder why he signed a contract extension with a term as long as that, I think he has almost two years to go.